v1.2.4: runs on Node 24

The action now declares node24. GitHub has deprecated Node 20 for actions and was already running this one on Node 24, with a deprecation warning in every workflow that used it. That warning is gone.

Validation is unchanged: dist/ rebuilds byte-identical to v1.2.3, and it still checks IntentSpec v1.2 with the same schema and anchor rules.

@v1 now points at this release. Nothing to change if you use @v1; bump to @v1.2.4 if you pin exact versions.